2-keto-levo-gulonic acid and process for the manufacture of same



act in asuitable manner with acetone.

Patented NovllO, 1942 UNITED STATES PATENT OFFICE.

z-xn'ro-Lsvo-ormomc son) s'ivnraoosss FOR THE MANUFACTURE or same mat.Reichsteln, Zurich, Switzerland, assignor to Hoflmann-La Roche Inc.,Nutle'y, N. 1., a corporation of New Jersey No Drawing. ApplicationOctober 18, 1934, Serial No. 748,925. In Switzerland October 25, 1933Claims. (01. sec-s40 0f the 2-keto-hexonic acids only tworepresentatives have so far been described, namely thell-teto-d-gluconic acid and the z-keto-d-gelactonic acid, and of theseonly the first mentioned has been thoroughly investigated. Two methodsfor obtaining representatives of these bodies have been described. Thefirst consists in oxidising cmon HO- -K onion le'vo-sorbose he xosoneswith bromine water (Biochemische Zeitschrift, 701. 207, 1929, pp. 217and 230) This j the necessary keto sugaraand secondly even with sugarshaving the hydroxyls in suitable position it could not be foretold,whether they would re- It was therefore not to be expected that it wouldbe possible to obtain a 2-keto-hexonic acid of the peculiar structure ofthe Z-keto-levo-gulonic acid, which is an important intermediary productfor the manufacture of levo-ascorbic acid (vitamin C). V Th process forthe levo-gulonic acid consists in transforming levosorbose with the aidof carbonyl compounds, such as formaldehyde, acetone,methyl-ethyl-ketone and the like, into the correspondingbis-methylene-ether-derivatives, treating these in alkaline solutionwith oxidising agents, which oxidise a manufacture of z-ketoinstancepermanganate, ierricyanide and the like, and heatig thebis-methylene-ether-2-ketolevo-gulonic acid, obtained from the solutionsby the addition of a trong acid, with water or dilute acids in order tosplit oi! the carbonyl compounds. The process is represented by thefollowing formulae, in which R. is a methylene radicle:

onion coon a -s a 110- --n J H:-O JJHr-0 onion n m w stance In thepresent process alterations in various directions may be made. Thus itis not at all necessary to isolate all the intermediary productsmentioned; The solution obtained by alkaline oxidation of thebis-methylene-ether-levo-sorbose may be transformed into the treebis-methylene-ether- 2-keto-levo-gulonic acid without isolating a salt.The isolation of this acid too may be eliminated by adding to thesolution of the crudeor pure salt at least as much of a strong acid asis necessary for freeing the bis-methylene-ether-ketoacid and thusobtaining the free 2-keto-levogulonic acid. Finally. if one wishes toobtain an ester, the separation of the tree 2-keto-levo-guionic acid inthe pure state may be left out altogether. Thus for instancediacetone-2-keto-levogulonic acid or one of its salts may be dissolvedin an alcohol with the addition of at least one molecule of water(advantageously not more than three molecules of water) and afterthe'addition of hydrochloric acid gas, sulphuric acid or the like leftto stand at room temperature or heated, until the transiormation hastaken place. When using free diacetone-keto-acida very small quantity ofhydrogen chloride gas is sufiicient; ii a salt is used, a quantitysuillcient for binding the base should be added. Otherdimethyleneether-derivatives oi 2-keto-levo-gulonic acid may be treatedin a similar manner; where the compounds are derived from aldehydes, theaddition of ,water for the separation is not necessary.

CHzOH group to the carboxyl group, such as ior The 2-keto-levo-gulonicacid is a strong acid I alcohol) forming colourless crystals melting at171' C. (cor-r.) with decomposition. Its specific rotation is [e]" --48(c.-1.0 in water). Boiling Fehling's solution is rapidly reduced by theacid. 2keto-levo-gulonie acid is the first of the 2-ketohexonic acids,which has been obtain in crystalline vform. Its salts and likewise itsesters are The esteriflca stance by heating the free acid with a largeexcess of an alcohol without any further addition, the transformationbeing performed by a continuous process inwhich from a boiling solutionof the components the alcohol laden-with the watervapour formed isdistilled ofl, dehydrated with a suitable drying agent aftercondensation and returned to the reaction receptacle. By the addition ofsuitable hydro-carbons, such as benzene, the process may be accelerated.The addition of mineral acids, toluene-sulphonic acid and the like alsohas an accelerating effect. The esters may further be obtained inquantitative yield by the reaction of the corresponding diam-aliphatichydrocarbons with a solution of the acid in the corresponding alcohol,or from a salt of the acid withalhl halides, alkyl sulphates orsulphites. The 2-keto-levo-gulonic-acid-methyl-ester forms colourlesscrystals melting at 155-157 C. Its specific rotation is [a] 25' (ca-1.0in methanol). The specific rotation of the ethylester is [aP =-14.5(c.-0.63 in absolute Example 1 1 kilogram of levo-sorbose, obtained fromsorbite'by oxidation with the aid of bacterium Xylinum, is. suspended inliters of acetone and after careful addition of 800 com. of concentratedsulphuric acid stirred for about 24 hours; the,

sugar will have dissolved before this time. The light yellow solution isneutralised in the usual manner with ammonia gas, anhydrous soda, potashor the like, made slightly alkaline, well dried some time. Furtherquantities are obtained by evaporating the mother liquors, flnally'alsoby the addition of ether. The yield is 1 to 1.1. kilogram. The saltmelts only above-300 C. with decomposition. Its specific rotation is[cr]" =13.8 (c.=1.08 in water). If the crude salt containing carbonateis to be further worked up, it will be suflicien't to wash it thoroughlywith ether, whereby small quantities of unchanged diacetone-sorbose areremoved.

1 kilogram of the potassium salt is dissolved in 2 liters oi water,about A kilogram of finely crushed ice is added and while stirringthoroughly a mixture oi V2 liter of per cent hydrochloric acid, /2 literof water and /z kilogram of finely crushed ice is likewise. added. Theacid is precipitated in leaflets. After-being left to stand for a shorttime it is removed by suction, well pressed out and washed three timeswith just the suflicient quantity of ice-water. From the mother liquorsand wash-waters the remnant may be obtained by quickly shakingwith-ether or ethyl acetate, if possible always in the presence offinely crushed ice. The yield is about 0.8 kilogram. The crystals haveno definite melting point. They contain one molecule of water ofcrystallisation, which is partly'removed by heating and partly causessplitting ofl of acetone. They sinter at about '75-'77 C. to a turbidmass, which clears only at about 95 C.v When being dried in high vacuumat room temperature they likewise become sticky and form a viscous mass.In the open. air or in closed tubes they seem to be more stable. Thecompound is a strong acid. which turns Congo-paper blue. Fehiing'ssolution is not reduced, unless the aqueous solution of the product isfirst heated and then only Fehiings solution added.

and after filtration the acetone is distilled ofl.

The residue distils in vacuo at 0.5 mm. and about 140 C. and forms acolourless, very viscous oil. A fraction of higher boiling pointcontains principally the mono-acetone-compound and by iurther treatmentwith acetone yields more'diacetone-sorbose. In the cold it sets to aglassy mass. Recrystallised from benzine, the diacetone-levosorboseforms colourless crystals melting at 77'I8 C. Its specific rotation is[a] =-18.1

(c.=1.38 in acetone).= It is easily soluble in or-,

- slum permanganate in 20 liters of water is added while stirring, thetemperature being kept at 30 C. The stirring is continued for about fourhours and alcohol is added until the colouration has disappeared. Theprecipitated manganese I dioxide is removed by filtration; carbondioxide 35 kilograms of sulphuric acid and 3.5 kilograms of water arevery thoroughly mixed together and I heated to 80 C. Aiter cooling iceis added and is passed into the clear solution until there is no morefree alkali, and hereafter the productis evaporated in vacuo to dryness.If the pure potassium salt is to be isolated, the residue is boiled withabsolute alcohol until the latter ceases to take up any more of theproduct. From the filtered solution the salt is precipitated in longneedles after cooling. and being left to stand for 800 grams of thediacetone compound are dissolved in 5-10 liters of water, heated toboiling point and then heated on the boiling water-bath until thesplitting of! 'of acetone is terminated, which will be in about 3M0minutes. The prodnot is then evaporated in vacuo to a thick syrup. whichon being scratched quickly crystallises. After complete crystallisationthe product is ground with acetone, the liquid removed by suction andwashed with acetone. A small second crop may be obtained from the motherliquors by evaporating in vacuo. The yield is about 520 rams.

Example 2 1 kilogram of powdered levosorbose, '5 kilograms oftri-hydroxy-methylene and a mixture of the solution poured into anexcess of ice-cooled strong potash-solution. The liquid is removed bysuction; the solid salts washed with a little'poti' ash-solution andmuch'chloroform, then the liquid portions are again shaken withchloroform. The solution is dried with sodium s'ulphate,'freed fromchloroform by distillation and the residue distilled in high vacuum.After a slight crystal lineflrst fraction in the bulk of di-formal-levm,sorbose distils at .a pressure of 0.2 mm. at'about' 132 C. and quicklycongeals. For purifyingthe product is recrystallised twice by dissolvingin hot benzene and adding the same volume of dry ether before it hasquite cooled down. The di-fornial levo-sorbose forms colourless crystalsmelting at 77-78" C. Its specific rotation is =-45.'l (c.=l.97 inwater). It is easily soluble in water;

. above 30 C. is prevented by cooling. The solu tion is freed frommanganese dioxide, saturated with carbon dioxide, evaporated in vacuo todryness and the residue boiled with absolute alcohol. From the filteredand evaporated solution a hygroscopicpowder is precipitated by theaddition of a great deal oi absolute ether.. This powder is washed withether, dissolved in ice-water and rendered very decidedly Congo-acid bythe addition oi strong hydrochloric acid and ice and shaken severaltimes with'acetic ester. After drying and evaporating the extracts leavea crystalline residue which is recrystallised from toluene. Thedi-iormal-z-keto-levo-gulonic acid melts at l29-l30 C. Its specificrotation is [l",,='43.25 (c.=l.04 in water). Thediiormal-2-keto-levo-gulonic acid is a great deal' more stable than theother bis-methylene-derivatins of 2-keto-levo-gulonic acid. It may beboiledi'or a considerable time with aqueous or dilute alcoholic mineralacids without decomposition. For the transformation into2-keto-levogulonic acid according to the method described in Example 1boiling at some length with dilute acids is necessary.

Example 3 l kilogram oi levo-sorbose, 22 kilograms ofmethyl-ethyl-ketone and 0.8 liters of concentrated sulphuric acid arestirred tor 20 hours. The unchanged levo-sorbose is filtered oil and thesolution treated in the same manner as when preparing the diacetonecompound (Example 1) The di-methyl-ethyl-ketone-levo-sorbosecrystallises in woolly needles melting at 96-99 C.

potassium permanganate in 14 liters oi water are I added and stirred.The iurther working up is the same as described in Example 1, 1or thedlacetone compound. The di-imethyl-ethyl-ketonel 2-keto-levo-gulonicacid is obtained in leaflets,

whichcontain one molecule of water of crystallisation and melt at about95-100 C. with decom-- 'position. The 2-keto-1evo-gulonic acid is prepred in the same manner as the diacetone-2- keto-levo-gulonic acid.

Example 4 50 kilograms oi benzaldehyde are poured over 2 kilograms offinely powdered levo-sorbose, 0.5 kilogram of hydrochloric acid gas ispassed in and the mixture stirred over night, whereby all the sugar isdissolved. The dark mixture is dissolved in ether, washed several timeswith dilute soda-solution, dried with sodium sulphate, freed from theether by distilling and from the benzaldehyde in high vacuum. The crudedi-benzal-levo-sorbose thus obtained is dissolved in'purifled pyridine,aqueous solutions oi potassium hydroxide and potassium permanganate areadded and shaken. The manganese dioxide is removed by suction, washedwith water and extracted with ether. The alkaline aqueous extracts areshaken with ether and the ethersolutions and the manganese-dioxideextracts united. The crude di-benzal-Z-keto-levo-guionicacid isseparated from the purified alkaline aqueous solution by the addition ofmineral acid and purified by repeated recrystallisation from boilingtoluene. It forms long colourless needles melting at 202-204" C. Fromthe di-benzal-2- keto-levo-gulonic acid the 2-keto-levo-gulonic acid isobtained by boiling for one hour with 10 parts oi alcohol and 10 partsn/5 aqueous hydrochloric acid.

The term carboxylic esters" as used in the claims is intended to meanesters of 2-keto-levo-v gulonic acid in which the carboxyl group hasbeen neutralized, as distinguished from other compounds in which otherhydroxy groups have been neutralized.

I claim:

1. The z-keto-levo-gulonic acid, which forms colourless'crystals meltingat 171 C. (corn) with decomposition, its specific rotation being [al'n=-48 (c.=1.0 in water), the said acid rapidly reducing boiling'Fehlings solution and being in the normal manner converted into itssalts and esters.

2. The process for the manufacture of 2-ketolevo-gulonic acid, whichconsists in transforming levo-sorbose with the aid of compounds selectedfrom the group consisting of aldehydes and ketones intobis-methylene-ether derivatives, treating these in alkaline solutionwith oxidising agents which oxidise a CHaOH group to a COOK group, andsplitting oi! the carbonyl compounds from thebis-methylene-ether-2-keto-levo-gulonic acids thus obtained by heatingwith water. the solution having an acid reaction.

3. The process for the manufacture of 2-ketolevo-gulonic acid, whichconsists in transforming levo-sorbose with the aid or acetone intodiacetone-levo-sorbose, treating the said diacetonelevo-sorbose inalkaline solution with oxidising agents which oxidise a CHzOH group to9. COOH group, and splitting oi! the acetone from thediacetone-2-keto-ievo-gulonic acid thus obtained by heating with water,the solution having an acid reaction.

4. The process for the manufacture oi 2-ketolevo-gulonic acid, whichconsists in transforming levo-sorbose with the aid of acetone intodiacetained by heating with water, the solution ha an acid reaction.

5. The process for the manufacture oiZ-ketolevo-gulonic acid, whichcomprises reacting levosorbose with a compound which iscapable orprotecting all the reactive hydroxyl radicals other than that of theterminal primary alcohol group contiguous to the keto group, oxidizingsuch terthan the terminal primary alcohol group contiguoua to the hategroup resistant to mild alkaline oxidation in solution, oxidizing suchterminal alcoholic group to a carboxyl group, and. then splitting 0d theremovable compound.

7. A substance selected from the group consisting of2-keto-levo-guloni'c acid, its salts obtainable by neutralization ordouble decompositlon oi the carboxylic' group and its carboxylic esters.

8. The lower alkyl esters of Z-keto-levo-gulonic acid.

9. A compound having the general formula COOH H t o .H V our-0 wherein Rrepresents the radical wherein X and Y are the same or difiereht mem'-.

bers of the group consisting of hydrogen, and, and aliphatic radicals.

10. A substance selected from t e group con sisting ofbis-methyIene-ether-Z-keto-levo-guionic acids and their salts obtainabletherefrom by neutralization or double decomposition.

acid.

12. The compound alpha-keto-l-gulonic acid. 13. The process for thepreparation of an a-keto-l-gulonic acid product which comprises treatingl-sorbose to oxidize its terminal keto alcohol group CO-GHzOH into thea-keto carboxylic acid group CO-GOOH with production of ana-keto-l-gulonic acid product capable of conversion into a producthaving the antiscorbutic properties of vitamin C.

14; An alpha-keto-l-gulonic acid product, the,

partial oxidation product of l-sorbose capable of conversion into avitamin 0 product;

15. The methyl ester of Z-keto-levo-gulonic acid.

TADEU'S REICHSTEIN.

11. A bis-methylene-ether-2-keto-levo-gulonic

